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From: Robert Haas <robertmhaas@gmail.com>
Date: Mon, 6 Apr 2026 10:55:02 -0400
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Subject: Re: pgsql: Reduce log level of some logical decoding messages from
 LOG to D
To: Fujii Masao <masao.fujii@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Thu, Apr 2, 2026 at 8:45=E2=80=AFPM Fujii Masao <masao.fujii@gmail.com> =
wrote:
> > If something goes wrong, enabling the messages for the future
> > won't tell you what went wrong in the past. I am wondering whether a
> > better approach might be to set the LOG level based on context -- that
> > is, if it's actually logical decoding, log this at LOG, but if it's
> > just someone peeking at a slot or similar, reduce the log level to
> > DEBUG1 or, really, probably more like DEBUG3.
>
> You are suggesting something like that logical walsender and
> pg_logical_slot_get_changes() should log at LOG, while the slotsync worke=
r
> should use DEBUG? Sorry, I may be misunderstanding, since the slotsync wo=
rker
> can also use logical decoding mechanism internally. Could you clarify wha=
t you
> have in mind by "peeking at a slot or similar"?

No, what I mean is that if someone runs an SQL function from the
foreground, they probably don't want that to result in a LOG message,
but if background activity results in such a message, the LOG message
is probably a good idea. The reasons are:

1. Somebody might run many foreground queries that rely on the logical
decoding infrastructure, so logging something every time such a query
is executed could produce a lot of log spam. But there shouldn't be so
much background logical decoding for this to be an issue.

2. If logical replication is not working, that may be a major issue
for the DBA. A problem running pg_logical_slot_get_changes() is likely
not as critical (and if it is, they can always lower
client_min_messages or log_min_messages for that session only).

--=20
Robert Haas
EDB: http://www.enterprisedb.com